Imprint technology is a development advanced from embossing technology well known in the art of optical disc production, which comprises pressing a mold original with an embossed pattern formed on its surface (this is generally referred to as “mold”, “stamper” or “template”) against a resin to thereby accurately transfer the micropattern onto the resin through mechanical deformation of the resin. In this, when a mold is once prepared, then microstructures such as nanostructures can be repeatedly molded, and therefore, this is economical, and in addition, harmful wastes and discharges from this nanotechnology are reduced. Accordingly these days, this is expected to be applicable to various technical fields.
Two methods of imprint technology have been proposed; one is a thermal imprint method using a thermoplastic resin as the material to be worked (for example, see S. Chou, et al., Appl. Phys. Lett. Vol. 67, 3114 (1995)), and the other is a photoimprint method using a photocurable composition (for example, see M. Colbun, et al., Proc. SPIE, Vol. 3676, 379 (1999)). In the thermal imprint method, a mold is pressed against a polymer resin heated up to a temperature not lower than the glass transition temperature thereof, then the resin is cooled and thereafter released from the mold to thereby transfer the microstructure of the mold onto the resin on a substrate. The method is applicable to various resin materials and glass materials and is expected to be applicable to various fields. For example, U.S. Pat. Nos. 5,772,905 and 5,956,216 disclose a imprint method of forming nanopatterns inexpensively.
On the other hand, in the photoimprint method where a composition for photoimprints is photocured by photoirradiation through a transparent mold or a transparent substrate, the transferring material does not require heating in pressing it against the mold, and therefore the method enables room-temperature imprinting. Recently, new developments having the advantages of the above two as combined, have been reported, including a nanocasting method and a reversal imprint method for forming three-dimensional structures.
For the imprint methods as above, proposed are applied technologies to nano-scale mentioned below.
In the first technology, the molded pattern itself has a function, and is applied to various elements in nanotechnology and to structural members. Its examples include various micro/nano optical elements and high-density recording media, as well as structural members in optical films, flat panel displays, etc. The second technology is for hybrid-molding of microstructures and nanostructures, or for construction of laminate structures through simple interlayer positioning, and this is applied to production of μ-TAS (micro-total analysis system) andbiochips. In the third technology, the formed pattern is used as a mask and is applied to a method of processing a substrate through etching or the like. In these technologies, high-precision positioning is combined with high-density integration; and in place of conventional lithography technology, these technologies are being applied to production of high-density semiconductor integrated circuits and transistors in liquid-crystal displays, and also to magnetic processing for next-generation hard discs referred to as patterned media. Recently, the action on industrialization of the above-mentioned imprint technologies and their applied technologies has become active for practical use thereof.
As an example of application of a nanoimprinting method, first described is a practical application thereof to formation of high-density semiconductor integrated circuits. Recently, semiconductor integrated circuits are being toward advanced micropatterning and increased density; and for realizing the intended micropatterning technology, high-accuracy photolithographic devices for pattern transfer are being much advanced. However, for satisfying the requirements for further more accurate micropatterning, the microprocessing method is being near to the wavelength of the light source in photoexposure, and the conventional lithographic technology is being near the end of its limit. Accordingly, in place of the lithographic technology for furthermore advanced micropatterning and further more increased accuracy, an electron-beam drawing system, a type of charged particle radiation system is being used in the art. The method of patterning with electron beams from such an electron-beam drawing system comprises a step of drawing via a mask pattern, different from the method for a one-shot exposure system of patterning with a light source such as an i-ray, an excimer laser or the like. Accordingly, when the number of the patterns to be drawn increases more, a longer time for photoexposure (drawing) is taken, and it is said that the defect with the method is that much time is taken for patterning. Therefore, with the drastic increase in the integration degree of semiconductor integrated circuits from 256 mega to 1 giga and to 4 giga, the patterning for them may take a drastically prolonged time, and the throughput may be thereby greatly lowered. Accordingly, for speeding up the patterning in the electron-beam drawing system, development of a one-shot irradiation exposure system, in which various shapes of masks are combined and are irradiated with electron beams all at a time to thereby form complicated electron beams, is being advanced. In this, the degree of micropatterning could be increased more, but the method is defective in that it requires a large-sized electron-beam drawing system and requires an additional mechanism of more accurately controlling the mask alignment, and therefore the apparatus cost for the method increases.
As opposed to this, as a technique of formation of micropatterns at a low cost, use of nanoimprint lithography technology (photonanoimprinting method) is under investigation. For example, Patent Document 1 and Patent Document 3 mentioned below disclose a nanoimprinting technology of forming a microstructure of at most 25 nanometers through pattern transfer using a silicon wafer as the stamper. Patent Document 4 mentioned below discloses a nanoimprinting composite composition applicable to the field of semiconductor microlithography.
Along the stream, investigations of production technology for micropatterning molds, mold durability, mold production cost, peelability of resin from mold, imprint uniformity, alignment accuracy and inspection technology for application of nanoimprinting lithography to the production of semiconductor integrated circuits are being much activated.
Next described is practical application of a photonanoimprinting method to flat displays such as liquid-crystal displays (LCD) and plasma displays (PDP).
With the recent tendency toward large-size and high-precision LCD substrates and PDP substrates, photonanoimprinting lithography as a type of inexpensive lithography has become specifically noted these days, in place of conventional photolithography for use in production of thin-film transistors (TFT) and electrode plates; and development of a photocurable resist in place of the etching photoresist for use in conventional photolithography has become necessary.
Also to the transparent protective film material for use for constructional elements in LCD and the like and to the spacer to define the cell gap in liquid-crystal displays, application of photonanoimprinting lithography is being investigated (for example, see Patent Documents 5 and 6). The resist for such constructional elements finally remains in the displays such as flat display panels, differing from the above-mentioned etching resist, and is therefore often referred to as “permanent resist” or “permanent film”.
The permanent film to which conventional photolithography is applied includes, for example, a protective film to be provided on the TFT substrate of a liquid-crystal panel, and a protective film to be provided on a color filter for reducing the difference in level between R, G and B layers and for making the color filter resistant to high-temperature treatment in formation of an ITO film through sputtering thereon. Heretofore, as a transparent permanent film for color filter, used is a photocurable resin or a thermosetting resin such as siloxane polymer, silicone polyimide, epoxy resin, acrylic resin or the like (see Patent Documents 7 and 8 mentioned below). In forming such a protective film (permanent film), the film is required to have various characteristics such as uniformity of the coating film, adhesiveness thereof to substrate, high transmittance thereof after heat treatment at a temperature over 200° C., as well as smoothness, solvent resistance and scratching resistance thereof.
In the field of spacers for use in liquid-crystal displays, a photocurable composition comprising a resin, a photopolymerizing monomer and an initiator is generally widely used in conventional photolithography (for example, see Patent Document 9). In general, the spacer is formed by patterning, on a color filter substrate after formation of color filter or formation of protective film for color filter thereon, a photocurable composition to form a pattern thereon having a size of from 10 μm to 20 μm or so, followed by post-baking under heat for curing it. The spacer for use in liquid-crystal displays is required to have various properties of high mechanical characteristics, hardness, developability, patterning accuracy, adhesiveness and the like.
Accordingly, it is desired to develop a photocurable composition favorable for forming a permanent film (permanent resist) such as the above-mentioned transparent protective film and spacer according to a nanoimprinting method.
With the tendency toward large-size substrates, a photocurable composition is required to satisfy coating film uniformity, and is much required to satisfy various severe requirements such as coating film thickness uniformity between the center part and the peripheral part of the substrate, and the dimensional uniformity for high resolution, and the requirements of the film thickness and the shape for the composition are being severer.
Heretofore, in the field of production of liquid-crystal display devices using a small-size glass substrate, a method of dropping a resist onto the center of the substrate followed by spinning it has been employed for resist coating (for example, see Non-Patent Document 3). However, the method of dropping onto the center followed by spinning the substrate could hardly satisfy the requirements except the coating uniformity. Accordingly, as an alternative technology, a novel resist coating method with a discharge nozzle system has become proposed, as applicable to large-size substrates after the fourth generation substrates, especially after the fifth generation substrates. In the resist coating method with a discharge nozzle system, the discharge nozzle and the substrate are relatively moved and a photoresist composition is applied on the entire surface of the substrate to be coated therewith; and for this, for example, proposed is a method of using a discharge nozzle system having a discharge port with a plurality of nozzle orifices aligned in lines or having slit-like discharge ports, through which a photoresist composition is discharged like strips, or a method of applying a photoresist composition onto the entire surface of a substrate to be coated therewith followed by spinning the substrate to control the thickness of the coating film. Accordingly, for application to the field of production of liquid-crystal display devices, a nanoimprinting curable composition is also required to satisfy coating uniformity thereof on substrates.
For improving the coatability with a positive photoresist, a pigment dispersion photoresist for color filter formation and a protective film for photomagnetic discs or the like, there is known a technique of adding various surfactants or the like to them (for example, see Patent Documents 10 to 17); and there is disclosed a case of using a photocurable resin that contains a fluorosurfactant as a photonanoimprinting etching resist for formation of semiconductor integrated circuits (for example, see Patent Document 18). Heretofore, however, no one knows a method for improving the coatability of a substrate with a nanoimprinting curable composition not containing pigment, dye and organic solvent as indispensable ingredients for a permanent film.
Further, in the photonanoimprinting method, the flowability of the photocurable composition in the cavity of the surface recesses of the mold having a pattern formed thereon, must be increased. In addition, the adhesiveness between the resist and the substrate (base, support) must be enhanced while the peelability between the mold and the resist is kept good. However, it is difficult to make the photonanoimprinting curable composition satisfy all the requirements of good flowability in the cavity, good peelability from the mold and good adhesiveness to the substrate.
The photocurable composition to be applied to nanoimprinting may be divided broadly into two types, a type of radical polymerization and a type of ionic polymerization, depending on the difference in the reaction mechanism therebetween, further including hybrid types of these. Curable compositions of all types are applicable to nanoimprinting; but because of the broad latitude thereof in material selection, in general, a radical polymerization-type curable composition is much used (for example, see Non-Patent Document 4). As the radical polymerization-type curable composition, generally used is a composition that contains a monomer or an oligomer having a radical-polymerizing vinyl group or a (meth)acrylic group, and a photopolymerization initiator. When irradiated with light, the radical-polymerizing curable composition undergoes chain polymerization as the radical generated by the action of the photopolymerization initiator thereon attacks the vinyl group, and therefore it forms a polymer. In case where a bifunctional or more polyfunctional monomer or oligomer is used, the composition may form a crosslinked structure. Non-Patent Document 5 mentioned below discloses a composition that comprises a low-viscosity, UV-curable monomer and can attain room-temperature imprinting.
The necessary properties of materials for photonanoimprinting lithography may often vary depending on the use thereof, but the materials may have some common features in point of the necessary process characteristics thereof irrespective of their use. For example, the main requirements shown in Non-Patent Document 6 mentioned below are coatability, adhesiveness to substrate, low viscosity (<5 mPa·s), peelability, low degree of curing shrinkage, rapid curability. Especially in the application field where low-pressure imprintability and reduction in film retention are required, the materials are much required to have a low viscosity. On the other hand, when the necessary characteristics are grouped for individual applications, for example, light refractivity and light transmittance are mentioned for optical members. For etching resists, the requirements are etching resistance and reduction in residual film thickness. It is a key point in material designing how to control the necessary characteristics and how to take the balance of the characteristics. Accordingly, the necessary characteristics greatly vary at least between a process material and a permanent film, and therefore the materials must be developed in accordance with the process and the application thereof. As a material to be applied to photonanoimprinting lithography, Non-Patent Document 6 mentioned below discloses a photocurable material having a viscosity of about 60 mPa·s (25° C.). Similarly, Non-Patent Document 7 mentioned below discloses a photosensitive fluororesin comprising a monomethacrylate as the main ingredient thereof and having a viscosity of 14.4 mPa·s, in which the peelability of the resin is enhanced.
Regarding compositions for photonanoimprinting, there are descriptions relating to the viscosity thereof as above; however, up to now, there is known no report relating the guideline for the planning of materials suitable to individual applications.
Patent Documents 19 and 20 mentioned below disclose a case of using a photocurable resin that contains an isocyanate group-having polymer and embossing it for formation of relief hologram or diffraction grating. Patent Document 21 mentioned below discloses a photonanoimprinting curable composition that contains a polymer, a photopolymerization initiator and a viscosity regulator.
Further, Non-Patent Document 8 mentioned below discloses examples of applying a photocurable radical-polymerizing composition that comprises (1) a polyfunctional acrylic monomer (2) a polyfunctional acrylic monomer, or (3) a combination of a polyfunctional acrylic monomer and a photopolymerization initiator, or a photocationic polymerizing composition that contains a photocurable epoxy compound and a photo-acid generator to nanoimprinting lithography, and checking them for thermal stability and mold releasability.
Non-Patent Document 9 mentioned below discloses a photonanoimprinting curable composition containing (1) a functional acrylic monomer, or (2) a functional acrylic monomer, a silicon-containing monofunctional acrylic monomer and a photopolymerization initiator, as a device to enhance the releasability between a photocurable resin and a mold and to solve the problem of film shrinkage after curing and sensitivity depression owing to photopolymerization retardation in the presence of oxygen.
Non-Patent Document 10 mentioned below discloses that use of a mold prepared by applying a photonanoimprinting curable composition that contains a monofunctional acrylic monomer, a silicon-containing monofunctional monomer and a photopolymerization initiator onto a silicon substrate followed by surface-treating it reduces pattern defects after molding. Non-Patent Document 11 mentioned below discloses that coating a silicon substrate with a photonanoimprinting curable composition that contains a silicon monomer, a trifunctional acrylic monomer and a photopolymerization initiator followed by SiO2 molding brings about a composition excellent in resolution and coating uniformity. Non-Patent Document 12 discloses a case of forming a pattern size of 50 nm with a cationic polymerizing composition that comprises a combination of a specific vinyl ether compound and a photo-acid generator. The composition is characterized by low viscosity and rapid curability, but they say that its problem is poor template peelability.
As shown in Non-Patent Documents 8 to 12, various photocurable resins applicable to photonanoimprinting lithography are disclosed, which comprise an acrylic monomer, an acrylic polymer and a vinyl ether compound differing in the functional group therein; however, any sufficient disclosure is given therein that relates to a guideline for preferred types, optimum monomers and monomer combinations for curable compositions, and for optimum viscosity of monomers or resists, solution properties of preferred resists, and planning of materials for improving resist coatability. Accordingly, nothing is known relating to a combination of preferred materials for widely applying curable compositions to photonanoimprinting lithography; and the actual condition is that a photonanoimprinting curable composition capable of exhibiting satisfactory performance in various applications is not as yet proposed up to now.
In Non-Patent Documents 11 and 12, some low-viscosity compositions are disclosed, but in case where they are patterned through photocuring followed by heat treatment, the transmittance of the final cured film is low (as colored) and the hardness thereof is low, and it could not be said that their practical performance as a permanent film could be sufficient.
Non-Patent Documents 13 and 14 propose an inorganic/organic hybrid material comprising a mixture of a photofunctional crosslinking substance-processed silica sol, (meth)acrylic monomer and a photopolymerization initiator, and report its application to photonanoimprinting lithography. Non-Patent Documents 13 and 14 report a case of 200-nm line pattern formation with an imprinting material and the patternability of the material up to a line width of 600 nm as a molding material. However, the material is still problematic in that its releasability from mold is insufficient and the hardness of the cured film is low, and therefore the material is not always satisfactory. Non-Patent Documents 13 and 14 disclose low-viscosity material compositions; however, the transmittance of the cured film formed by patterning the composition through photocuring followed by heat treatment is low (that is, the cured film is colored), and the hardness thereof is low.
Patent Document 22 discloses a patterning method using a fluorine-containing curable resin for bettering the releasability from mold, and discloses a hard coat composition containing a surface-treated colloidal silica, a specific (meth)acrylic monomer, a leveling agent and a photopolymerization initiator; and this reports application of the composition to optical discs that satisfy both film hardness and curing shrinkage resistance. However, the composition is still insufficient in point of the releasability from mold and the substrate coatability thereof, and its application to photonanoimprinting lithography is difficult. Further, in case where the composition is heat-treated after photocuring, the resulting pattern is colored, its transmittance is low and therefore the composition is unsuitable to a permanent film that requires light transmittance.
Patent Document 23 mentioned below discloses a nanoimprinting photocurable composition that comprises a cyclic structure-having (meth)acrylate monomer for making the composition etchable in dry. However, when the composition is photo-cured and then heat-treated, the transmittance of the resulting film is also low as the film is colored, and the composition is hardly used for a permanent film that requires light transmittance, and in addition, the hardness and the solvent resistance of the cured film is insufficient.
On the other hand, Patent Document 24 mentioned below discloses a curable composition containing an aromatic alkenyl ester, and discloses the effect of allyl ester benzoate for viscosity reduction.
Patent Document 25 discloses an curable composition for inkjet that comprises a monomer having a photopolymerization site and a thermal reaction site in one molecule.
Patent Document 26 discloses a curable composition with an acrylate monomer having a vinyl ether group in one molecule.
As in the above, there are a lot of essential technical themes with a permanent film, such including, for example, patterning accuracy, adhesiveness, transparency after heat treatment at higher than 200° C., high mechanical property (strength against external pressure), scratching resistance, surface smoothness, solvent resistance and outgassing reduction in heat treatment. In case where a photonanoimprinting curable composition is applied to a permanent film, its important requirements are (1) uniformity of coating film, (2) transparency after heat treatment and (3) scratching resistance, like conventional resists with an acrylic resin.
In addition, the subject theme peculiar to photonanoimprinting curable compositions is that, in addition to the above (1) to (3), (4) the flowability of the resist composition in the recesses of mold is secured and the composition must have a low viscosity in the absence of a solvent or in the presence of a small amount of a solvent, and (5) after photocured, the film is readily peeled from the mold with no stickiness to the mold, and these must be taken into consideration, and the technical difficulty in planning the composition is thereby further increased.
A composition heretofore known for inject application and for protective film for photomagnetic discs, and a photonanoimprinting curable composition used as an etching resist may have some material intersections with photonanoimprinting curable compositions for use for formation of permanent films, but they significantly differ in point of the necessary properties thereof such as high-temperature heat treatment applicability and mechanical strength. Accordingly, in case where a photocurable resin for protective film for photomagnetic discs or for etching resists is directly used as a resist for a permanent film, then the resin could not provide a practicable film in point of the transparency, the mechanical strength and the solvent resistance. As in the above, though various materials are disclosed for photonanoimprinting curable compositions, but at present, any satisfactory guideline for planning a curable composition suitable for formation of a permanent film is not as yet shown.    [Patent Document 1] U.S. Pat. No. 5,772,905    [Patent Document 2] U.S. Pat. No. 5,956,216    [Patent Document 3] U.S. Pat. No. 5,259,926    [Patent Document 4] JP-T-2005-527110    [Patent Document 5] JP-A-2005-197699    [Patent Document 6] JP-A-2005-301289    [Patent Document 7] JP-A-2000-39713    [Patent Document 8] JP-A-H6-43643    [Patent Document 9] JP-A-2004-240241    [Patent Document 10] JP-A-7-230165    [Patent Document 11] JP-A-2000-181055    [Patent Document 12] JP-A-2004-94241    [Patent Document 13] JP-A-H4-149280    [Patent Document 14] JP-A-H7-62043    [Patent Document 15] JP-A-2001-93192    [Patent Document 16] JP-A-2005-8759    [Patent Document 17] JP-A-2003-165930    [Patent Document 18] JP-A-2007-84625    [Patent Document 19] JP-A-2004-59820    [Patent Document 20] JP-A-2004-59822    [Patent Document 21] JP-A-2006-114882    [Patent Document 22] JP-A-2000-143924    [Patent Document 23] JP-A-2007-186570    [Patent Document 24] JP-A-H10-251473    [Patent Document 25] WO2004/099272    [Patent Document 26] JP-A-2005-255854    [Non Patent Document 1] S. Chou et al.: Appl. Phys. Lett. Vol. 67,3114(1995)    [Non Patent Document 2] M. Colbun et al: Proc. SPIE, Vol. 3676, 379 (1999)    [Non Patent Document 3] Electronic Journal 121-123 No. 8 (2002)    [Non Patent Document 4] F. Xu et al.: SPIE Microlithography Conference,5374, 232(2004)    [Non Patent Document 5] D. J. Resnick et al.: J. Vac. Sci. Technol. B, Vol. 21,No. 6, 2624(2003)    [Non Patent Document 6] The latest resist material hand book, P1, 103-104(200, Johokiki Publishing)    [Non Patent Document 7] CMC Publishing Co., Ltd: Development and Apply of Nanoimprints, P159 to 160 (2006)    [Non Patent Document 8] N. Sakai et al.: J. Photopolymer Sci. Technol. Vol. 18, No. 4, 531(2005)    [Non Patent Document 9] M. Stewart et al.: MRS Buletin, Vol. 30, No. 12, 947(2005)    [Non Patent Document 10] T. Beiley et al.: J. Vac. Sci. Technol. B18(6), 3572(2000)    [Non Patent Document 11] B. Vratzov et al.: J. Vac. Sci. Technol. B21(6), 2760(2003)    [Non Patent Document 12] E. K. Kim et al.: J. Vac. Sci. Technol, B22(1),131(2004)    [Non Patent Document 13] Proc. SPIE Int. Soc. Opt. Eng., Vol. 6151, No. Pt2, 61512F(2006)    [Non Patent Document 14] Science and Industry, Vol. 80, No. 7, 322(2006)